1. Field of the Invention
The present invention generally relates to a powder conveyance device to convey powder such as toner from a powder container to a destination and an image forming apparatus such as a copier, a printer, a facsimile machine, a plotter, or a multifunction machine capable of at least two of these functions that includes the power conveyance device.
2. Discussion of the Background Art
In general, electrophotographic image forming apparatuses such as copiers, printers, facsimile machines, or multifunction machines including at least two of these functions include a development device to develop latent images formed on an image carrier, and a toner conveyance device to convey powdered toner to the development device from a replaceable toner bottle.
Such toner conveyance devices typically include a toner container, a toner discharge member to discharge toner from the toner container, and conveyance means such as a conveyance pipe that connects the toner container to the development device. The toner discharge member is operated as required to discharge toner from the toner container to the conveyance pipe, and the toner is supplied through the conveyance pipe to the development device.
In image forming apparatuses using such a toner conveyance device, when the toner container is positioned lower than the development device, powdered toner discharged to the conveyance pipe must be conveyed upward against the force of gravity to the development device, an arrangement that has the effect of reducing efficiency in toner conveyance. Additionally, such a configuration can increase the possibility of clogging of the conveyance pipe with toner. Therefore, the toner container is generally disposed above the development device so that toner can be transported downward in the direction of gravity.
For example, JP-H08-30097 discloses such a toner conveyance device for transporting toner in the direction of gravity. This toner conveyance device includes a toner box serving as the toner container, the conveyance pipe, and the toner discharge member that discharges toner from the toner box to the conveyance pipe. Toner drops under gravity through the conveyance pipe to the development device.
However, in this toner conveyance device, it is possible that the toner discharged from the toner box accumulates in the conveyance pipe and a relatively large amount of toner might flow to the development device at one time, a phenomenon hereinafter referred to “uncontrolled flow of toner”. For example, if toner flows uncontrollably into development devices using two-component developer consisting essentially of toner and magnetic carrier, it is difficult to adjust the toner concentration in the two-component developer properly. Additionally, in development devices using one-component developer consisting essentially of only toner, if a relatively large amount of toner flows to the development device at one time, the proportion of toner particles having insufficient electrical charge in the developer increases suddenly, which can cause image failure in which insufficiently charged toner particles adhere to a non-image area of the image carrier. Occurrence of uncontrolled flow of toner may be prevented by disposing the toner box and the development device relatively close to each other, thereby reducing the length of the conveyance pipe because the amount of toner accumulated in the conveyance pipe can be reduced accordingly. However, such limitations reduce design flexibility in layout in the image forming apparatus.
In view of the foregoing, JP-2005-24665-A proposes using a coil to transport the toner and a bar-shaped powder conveyance regulator that restricts passage of toner inside the conveyance pipe, both disposed inside the conveyance pipe, in order to keep the amount of supplied toner constant without sacrificing flexibility in the layout.
However, although effective for reliable toner supply to some extent, this approach has several drawbacks. For example, in multicolor image forming apparatuses, when fluidity (degree of agglomeration) of toner is different among the different color toners or limitations in layout cause differences in the configuration (shape, length, etc.,) of the toner conveyance path for the respective color toners, the amount of toner supplied to the development device (hereinafter “toner supply amount”) may be different among the different color toners or become insufficient because of the powder conveyance regulator.
Moreover, in modification of existing image forming apparatuses to achieve higher image quality, if the type of toner used therein is changed, similar problems may arise due to differences in fluidity (degree of agglomeration) between the toner used in the existing apparatus and that used in the modified apparatus. In this case, it is preferable that a dedicated toner conveyance regulator be designed for each color, for each toner conveyance path, and for each modification of the apparatus.
In view of the foregoing, the inventor of the present invention recognizes that there is a need for a powder conveyance device capable of adjusting the toner supply amount in accordance with conditions such as differences in fluidity of powder (toner), the length of the conveyance path, etc.